In a nitride semiconductor light emitting device, hydrogen is undesirably included in a p-type nitride semiconductor layer upon fabrication of the p-type nitride semiconductor layer. At this time, the p-type nitride semiconductor layer has the property of an insulator, but not the property of a semiconductor due to hydrogen. It is thus required that an additional activation annealing process for eliminating hydrogen be performed after the p-type nitride semiconductor layer has been formed.
As shown in FIG. 3, U.S. Pat. No. 5,306,662 discloses a method for eliminating hydrogen through annealing at a temperature of over 400° C. after a p-type nitride semiconductor layer has been grown. U.S. Pat. No. 5,247,533 presents a method for forming a p-type nitride semiconductor layer through electron beam illumination.
In case of electron beam illumination, however, it is difficult to form a uniform p-type nitride semiconductor layer. In case of annealing, an underlying active layer may be thermally damaged due to the annealing process. Therefore, there is a high possibility that the performance of devices can be degraded.
Meanwhile, U.S. Pat. No. 6,043,140 proposes a method for fundamentally prohibiting introduction of hydrogen upon growth of p-type GaN by using a nitrogen precursor and a nitrogen carrier from which hydrogen is not generated. It is, however, difficult to obtain satisfactory surface morphology through this method. This method can be considered a reasonable approach in terms of the principle. In an actual application, however, specially, in terms of mass production of a commercial light emitting device, this method is considered an unpractical technology. Moreover, the cost of a hydrazine based source is greatly expensive as compared with ammonia. In this connection, it is considered that the competitiveness in the cost of the commercial light emitting device may be lost.
FIG. 1 is a cross-sectional view illustrating the structure of a conventional AlGaInN based LED.
A method for the conventional AlGaInN based LED will be below described in short. A nitride semiconductor light emitting device includes a buffer layer 11, a semiconductor layer 12 composed of a n-type nitride semiconductor, an active layer 13 composed of a nitride semiconductor that emits light through recombination of electrons and holes, and a semiconductor layer 14 composed of a p-type nitride semiconductor, all of which are sequentially grown on a substrate 10.
Thereafter, an activation annealing process is performed wherein hydrogen contained in the nitride semiconductor layer 14 is stripped at a high temperature of 400° C. or more. An electrode layer 15 is then formed on the nitride semiconductor layer 14 that is electrically brought into contact with the electrode layer 15. The nitride semiconductor layer 14 and the active layer 13 are mesa-etched to expose the nitride semiconductor layer 12. An n-type electrode layer 16 is formed on the nitride semiconductor layer 12 and a bonding pad 17 is then formed on the electrode layer 15. Finally, a protect film 18 is formed.
The bonding pad 17 is usually formed on the electrode layer 15, but may be directly formed on the nitride semiconductor layer 14 after some of the electrode layer 15 has been removed. An n-type nitride semiconductor layer of a high concentration or a superlattice layer made of an nitride semiconductor can be inserted between the nitride semiconductor layer 14 and the electrode layer 15 in order to form a tunnel junction therebetween. The substrate 10 is formed using sapphire, SiC, GaN, AlN or the like, but may be formed using any kind of a material on which a nitride semiconductor layer can be grown.
In order to fabricate such a light emitting device, single crystal growth is required. A MOCVD (Metal Organic Chemical Vapor Deposition) method is usually used. In this case, as shown in FIG. 2, ammonia (NH3) is used as a supply source of nitrogen (N) for growing GaN. In growing GaN, H2 is usually used as a carrier gas. In order to grow InGaN, N2 is usually used as a carrier gas.
Ammonia (NH3) is very thermally stabilized. Thus, only several % of NH3 is thermally decomposed at a temperature of over 1000° C. and this decomposed ammonia (NH3) contributes to growth of GaN as a nitrogen (N) supply source. Accordingly, in order to increase efficiency of thermal decomposition, high temperature growth is inevitably needed. Ammonia (NH3) also has a very high NH3/Ga ratio, which is required in order to obtain GaN having a good crystallization property.
A large amount of NH3 generates a large amount of hydrogen as a byproduct. In this case, when p-type GaN is grown, hydrogen is combined with magnesium as a p-type dopant, resulting in a magnesium (Mg)-hydrogen (H) atomic bonding. Thus, magnesium (Mg) does not produce holes and the p-type GaN does not have the property of a semiconductor.
Therefore, after the p-type GaN has been grown, it experiences a subsequent annealing process for breaking the magnesium(Mg)-hydrogen (H) atomic bonding at a temperature of 400° C. or more. For this reason, Mg provides holes and the p-type GaN has the property of a semiconductor.
As described above, the conventional nitride semiconductor light emitting device requires electron beam illumination or a process for annealing at a high temperature of over 400° C. in order to obtain p-type GaN of a high quality. However, this makes the process complicated and the active layer 13 is thermally damaged during the annealing process. Resultantly, there is a high possibility that the performance of a device may be degraded.
Disclosure
Technical Problem
Accordingly, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an AlGaInN based optical device in which an additional subsequent annealing process for eliminating hydrogen is not needed by preventing hydrogen from being contained in an nitride semiconductor layer when a p-type nitride semiconductor layer is grown, and method for manufacturing the same.
Technical Solution
To achieve the above object, according to one aspect of the present invention, there is provided an AlGaInN based optical device including a p-type nitride semiconductor layer that is grown using NH3 as a nitrogen precursor, wherein the p-type nitride semiconductor layer is grown using both NH3 and a hydrazine based source as the nitrogen precursor.
Furthermore, the AlGaInN based optical device according to the present invention may further include an active layer that emits light through recombination of electrons and holes, wherein the p-type nitride semiconductor layer supplies holes to the active layer.
In addition, in the AlGaInN based optical device according to the present invention, radicals generated when the hydrazine based source is thermally decomposed may include at least one of CH3 and NH2.
Furthermore, according to another aspect of the present invention, there is also provided a method for manufacturing an AlGaInN based optical device, including the step of growing a p-type nitride semiconductor layer using NH3 as an nitrogen precursor, wherein the step includes growing the p-type nitride semiconductor layer using both NH3 and a hydrazine based source as the nitrogen precursor.
In addition, in the method for manufacturing the AlGaInN based optical device according to the present invention, a carrier gas of the nitrogen precursor may be at least one of nitrogen and hydrogen.
Also, in the method for manufacturing the AlGaInN based optical device according to the present invention, the hydrazine based source may be at least one of monomethylhydrazine, dimethylhydrazine and tertiarybutylhydrazine.
Advantageous Effects
According to the present invention, an additional subsequent annealing process for extracting hydrogen is not necessary. Therefore, a process is simple and an active layer can be prevented from being thermally damaged by subsequent annealing.
Furthermore, according to the present invention, it is possible to obtain a nitride semiconductor layer of a p-type without a subsequent annealing process and to form a p-type nitride semiconductor layer having morphology of the degree required by a light emitting device.